|Publication number||US7814772 B2|
|Application number||US 11/987,348|
|Publication date||Oct 19, 2010|
|Filing date||Nov 29, 2007|
|Priority date||Nov 29, 2007|
|Also published as||CN101878086A, CN101878086B, EP2225066A1, EP2225066B1, US20090139291, WO2009068733A1|
|Publication number||11987348, 987348, US 7814772 B2, US 7814772B2, US-B2-7814772, US7814772 B2, US7814772B2|
|Inventors||Osmo Mikkola, Timo Norvasto, Pirjo Virtanen|
|Original Assignee||Metso Minerals, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (15), Non-Patent Citations (1), Referenced by (1), Classifications (38), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates to a method for manufacturing a coiler drum and to a coiler drum.
Reversing hot mills, also called Steckel mills, are used as hot strip mills for hot-rolling slabs of stainless steels, special steel, etc.
On opposite sides of the rolling mill 1 there are arranged two coiler furnaces 4. When processing the strip with the rolling mill 1, it is alternately wound up on and unwound from the opposed coiler furnaces 4, each comprising a rotating, cylindrical coiler drum 5. The purpose of the coiler furnaces is to maintain the temperature of the strip between passes through the nip N. The coiler furnaces are maintained at a temperature, for example, of about 900 to about 1050░ C.
In operation, the strip 3 passing through the nip N is led to the nearer coiler furnace 4 and wound onto its respective coiler drum 5. Subsequently, the strip 3 is unwound from the coiler drum 5 as the strip is fed back through the nip N. The process passing the strip through the nip N and winding and unwinding it is repeated until a desired thickness of the strip is reached.
A coiler drum is a hollow cylinder having an outside diameter of at least about 1000 mm, a length of about 2000 to 5000 mm and a great wall thickness of about 30 to 150 mm. The coiler drum is usually prepared by casting of a heat resistant alloy. The working surface of a coiler drum, that is the surface that becomes next to the strip to be wound, is usually flat or grooved.
As can be realized from the description above, the coiler drum is working in a very harsh environment. The temperature in the coiler furnace is high. The surface of the coiler drum is also repeatedly subjected to high tightening force when winding the steel strip on the drum. This causes fatigue fractures or other cracks to the surface of the coiler drum. The coiler drums also blister. These influence the durability of the coiler drum. They also leave marks on the steel strip that is being manufactured, thus deteriorating the quality of the product. The surface of the coiler drum is also exposed to an iron oxide film formed on the surface of the steel strip when rolling up the steel strip. In spite of descaling, part of the iron oxide film transfers on and sticks to the coiler drum and subsequently causes defects to the strip. This deteriorates the quality of the product.
Nowadays the problems caused by the blisters in the coiler drum surface are solved by shutting down the furnace so that the blisters can be hand-ground to reduce the blisters. The frequent shut downs result in high operating costs for maintaining the rolls and reduction of product throughput capability.
The coiler drums also tend to sag at current operating temperatures, which prevents operating the furnace at even higher temperatures. The sagging causes the drums to become eccentric in their rotation. This causes uneven revolving of the drum, which has an influence on the operation and durability of the coiler furnace and causes defects on the strip. Sagging also causes deformations, i.e. narrowing the slot of the coiler drum. As a consequence, the coiler drum has to be replaced.
The above mentioned problems have been tried to overcome by using different cast steel compositions when casting the coiler drums. One example is disclosed in U.S. Pat. No. 6,033,626. The composition presented in the patent is only a variation of a standard steel composition. It is soft in high temperatures in which the coiler drums are being used and thus there are problems caused by the deformation of the coiler drum. Also it can not refrain the blistering of the surface of the coiler drum.
US published patent application 2001/0013383 discloses a trinickel aluminide-based heat resistant alloy for a material for hearth rolls for heating furnaces. The material has a high creep rupture strength in temperature ranges over 1050░ C. and excellent weldability. The problem is that trinickel aluminide-based materials are expensive. The material is suitable for casting rolls with a simple structure, i.e. a hollow cylinder, but it can not be used to cast objects with complex geometrical structures, such as a coiler drum. Moreover, when preparing the molten trinickel aluminide alloy, the reaction is strongly exothermical. Thus it is not possible to cast objects that are as big in size as coiler drums are.
Both of these patent publications disclose casting the entire drum or roll from the same material and as one piece.
The purpose of the present invention is thus to provide a method for manufacturing a coiler drum and a coiler drum, which method and coiler drum avoid the above-mentioned problems and by means of which the durability of the coiler drum can be increased remarkably and the quality of the product produced by a rolling mill can be improved.
The invention is based on the idea that the coiler drum is manufactured in such a way that it comprises forming a trinickel aluminide containing surface layer on a coiler drum body.
The trinickel aluminide alloy can be formed on the coiler drum body by welding or thermal spraying. The surface layer may also be a sleeve of trinickel aluminide alloy that is arranged on the body. The thickness of the surface layer is from about 0,1 mm to about 8 mm, suitably from about 1 mm to about 4 mm. The surface layer defines a working surface that will engage a strip of metal when it is being rolled on the coiler drum.
The surface layer may be produced to be smooth and even against the steel strip to be wound. The surface layer can be formed on the coiler drum as raised strips of trinickel aluminide alloy extending radially outward from the base surface of the coiler drum body. These raised strips define a working surface that will engage a strip of metal when it is being rolled on the coiler drum.
The invention has many advantages. Trinickel aluminide alloy has high temperature strength and high temperature corrosion resistance. Consequently, when the surface layer is made from trinickel aluminide alloy, the surface hardness is excellent in high temperatures. When using a conventional H-series austenitic alloy as the surface material, the surface hardness decreases as the temperature increases. It has been noticed that the high surface hardness of trinickel aluminide alloy lasts through the lifetime of a coiler drum in high temperatures. It has also been noticed that the sticking of the iron oxide from the product to the coiler drums is reduced or eliminated, which reduces the pitting marks on the strips. Thus, the quality of the end product is better and the yield from slab to the product is higher. The working life of the coiler drum is also increased because of the high durability in high temperatures. The deformations of the drum are reduced which also increases its lifetime.
It is also possible to manufacture the coiler drum body from a lower cost material and use the expensive trinickel aluminide material only for forming the surface layer. This reduces the price of the coiler drum. Also by using a material having a high yield strength in the drum body and a trinickel aluminide-based surface layer on it, it is possible to improve the drum's strength against local stresses and to prevent drum breakages and deformation.
When using a structure where the surface layer is welded on the coiler drum body, it has been noticed in high temperature FEA analysis that the welded surface structure reduces the temperature gradient in coiler drum wall. This results in lower combined stresses and prevents the drum breakage and deformation.
In the following, the present invention will be described in more detail with reference to the appended figures, in which
In this description and claims the term casting means pouring a molten steel alloy to a casting mould where it is solidified as it is cools down. The molten alloy retains the form defined by the casting mould when it cools down. The casting mould can be either stationary or it can rotate in the axial direction during casting. Rotating casting moulds are used to cast axially symmetrical objects, such as cylinders, rolls or pipes.
In one embodiment of the invention, a surface layer 7 of trinickel aluminide (Ni3Al) alloy is provided on the coiler drum body 6. The surface layer covers the coiler drum substantially completely, extending, in the axial direction of the coiler drum, from one end of the coiler drum to the other end and defining a working surface 9 that will engage the strip of metal when it is being processed in a reversing rolling mill. It also covers the coiler drum body around its entire circumference. In
The surface layer can also be a sleeve of trinickel aluminide alloy that is arranged on the body. The sleeve may be prepared from a sheet of trinickel aluminide alloy having a suitable thickness. The sheet is processed to a sleeve of appropriate size and it is fitted on the drum body. The sleeve is attached to the coiler drum body by welding.
In another embodiment of the invention, the coiler drum 5 comprises a plurality of raised strips of trinickel aluminide alloy extending radially outward from the base surface of the coiler drum body.
The orientation of the raised strips 10 on the base surface 11 relative to the coiler drum may vary. In the embodiment shown in
The height H of the raised strips is about 2 to about 10 mm, suitably from about 4 to about 8 mm. The raised strips 10 have a flat upper surface. When winding the metal strip 4 on the coiler drum 5, the upper surfaces of the raised strips 10 form the working surface 9 that will engage the strip of metal when it is being processed in a reversing rolling mill.
The trinickel aluminide alloy consists of, in % by weight,
The coiler drums that are manufactured according to the invention are especially suitable for use in Steckel Mill coiler furnaces.
The intention is not to restrict the invention to the embodiments described by way of example, but it is intended that the invention can be interpreted widely within the scope of protection defined by the claims presented hereinbelow.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
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|U.S. Classification||72/148, 492/30, 72/47, 242/610.5, 242/600|
|International Classification||B65H75/14, B21C47/00|
|Cooperative Classification||B23K2203/50, B23K26/32, B23K26/342, Y10T29/49544, C22C19/051, C22C19/056, C23C28/021, B21C47/28, B32B15/015, B23K9/048, B23K2201/34, B23K2203/16, C23C30/00, C22C19/05, C22C19/03, C23C26/02, B23K10/027, C23C4/08, B23K2201/04, B23K35/0238|
|European Classification||B23K9/04D2C, C23C4/08, B32B15/01D1, B21C47/28, C22C19/03, C23C30/00, C22C19/05, C23C28/02B, C23C26/02, B23K26/34, B23K10/02H|
|Feb 20, 2008||AS||Assignment|
Owner name: METSO LOKOMO STEELS OY, FINLAND
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MIKKOLA, OSMO;NORVASTO, TIMO;VIRTANEN, PIRJO;REEL/FRAME:020567/0425;SIGNING DATES FROM 20080104 TO 20080107
Owner name: METSO LOKOMO STEELS OY, FINLAND
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MIKKOLA, OSMO;NORVASTO, TIMO;VIRTANEN, PIRJO;SIGNING DATES FROM 20080104 TO 20080107;REEL/FRAME:020567/0425
|Oct 9, 2009||AS||Assignment|
Owner name: METSO MINERALS, INC., FINLAND
Free format text: CHANGE OF NAME;ASSIGNOR:METSO LOKOMO STEELS OY;REEL/FRAME:023349/0914
Effective date: 20071231
|Apr 10, 2014||FPAY||Fee payment|
Year of fee payment: 4
|Jul 17, 2015||AS||Assignment|
Owner name: TEVO OY, FINLAND
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:METSO MINERALS, INC.;REEL/FRAME:036118/0835
Effective date: 20150413